Paper No. 78-3
Presentation Time: 8:40 AM
DEVELOPING TRIPLE OXYGEN ISOTOPE GEOCHEMISTRY AS A CENOZOIC PALEOALTIMETER USING CRYSTALLINE AND LACUSTRINE ROCKS (Invited Presentation)
IBARRA, Daniel1, METHNER, Katharina2, KUKLA, Tyler3, LLOYD, Max4, STOLPER, Daniel A.5, GAO, Yuan6, DAI, Jingen6, MULCH, Andreas7 and CHAMBERLAIN, C. Page8, (1)Institute at Brown for Environment and Society, Brown University, Providence, RI 02912; Department of Earth, Environmental and Planetary Sciences, Brown University, Providence, RI 02912, (2)Stanford University, Stanford, CA 94305-4121, (3)Geosciences, Colorado State University, Fort Collins, CO 80521, (4)Penn State University, University Park, PA 16802, (5)Department of Earth and Planetary Sciences, University of California Berkeley, Berkeley, CA 94720, (6)China University of Geoscience Beijing, Beijing, 100083, China, (7)Senckenberg Biodiversity and Climate Research Centre, 60325 Frankfurt, Germany, Goethe University Frankfurt, Institute of Geosciences, Frankfurt, 60438, Germany; Senckenberg Research Institute, Biodiversity and Climate Research Centre, Senckenberganlage 25, Frankfurt Main, 60325, Germany, (8)Geological Sciences, Stanford University, Stanford, CA 94305
Triple oxygen isotopes of minerals preserved in lacustrine sediments and hydrothermally altered minerals from crystalline rocks can be used to determine past elevations of mountain ranges as they may preserve an isotopic record of ancient precipitation. Here we use the measurement of all three stable isotopes of oxygen (16O, 17O, and 18O) to create data trends in 17O/16O vs 18O/16O that are extrapolated back to the meteoric water line using water/rock mixing constraints and models for lake water evaporation. We summarize recent advances in this approach and focus on examples from Cenozoic western North America and Tibet.
Three key findings emerge from our analysis of hydrothermally-altered crystalline rocks and lacustrine systems. First, in combination with carbonate clumped isotope measurements we demonstrate that Eocene lacustrine chert forms during early burial diagenesis at temperatures <60 °C. Importantly, these Eocene lacustrine cherts still preserve signals of ancient evaporative lake systems demonstrating δ’17O-δ’18O mass laws shallower than Rayleigh-dominated meteoric processes. These relationships still allow for past paleoelevation to be reconstructed. Second, we compare this approach to prior work that jointly used oxygen and hydrogen isotopes to determine the isotopic composition of meteoric waters. Our analysis suggests that hydrogen isotopes may exchange with ambient fluids in some systems but not others and is dependent on mineralogy and cooling rate. Further, through a quantitative model, we show that chert oxygen isotopes are not as susceptible to this alteration. Third, hydrothermal system and core-complex based paleoaltimetry constraints agree well with carbonate and clay-based estimates from nearby age-equivalent sedimentary basins. This new tool is nascent but provides complementary information to be used in conjunction with more traditional isotope-based paleoaltimetry approaches.
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